The present invention relates to the removal of harmful or undesired contaminants from polymer solutions, particularly from polycarbonate polymer solutions, using a strong acid cation exchange resin.
In the prior art, there are several known methods of removing contaminants or undesired by-products, particularly organic contaminants such as pyridine hydrochloride, from polymer solutions, such as polycarbonate polymer solutions. The presence of residual amounts of such impurities in the polymer usually renders the polymer less stable to heat and affects the clarity and light transmission properties thereof. Generally, the prior art is directed to the use of a multi-stage water wash to achieve a polycarbonate polymer solution containing impurities in the parts per million (ppm) level desired.
Other methods, such as set forth in U.S. Pat. No. 3,144,432, concern the use of certain materials in the preparation of the polycarbonate solution which act as non-solvents for the pyridine hydrochloride impurity. Such non-solvents cause the impurity to precipitate, therefore enabling easy separation of the same from the polymer solution. However, such method does not completely remove the impurity and the polymer solution must be subjected to time-consuming distillation to remove substantially all of the residual impurity. Another impurity precipitation method is disclosed in U.S. Pat. No. 3,437,639, wherein excess tertiary amine in a polycarbonate solution is precipitated by use of a hydrogen halide gas and non-solvent.
It is, therefore, an object of this invention to provide a novel and improved method for removing undesired organic contaminates from polymer solutions. Another object is to provide a novel and improved method for removing undesired pyridine hydrochloride from polycarbonate polymer solutions.